Multiple hammer magnetic pole piece block

ABSTRACT

A print hammer actuating assembly for a high speed printer, wherein a one-piece magnetic block is secured to a first core structure to provide a second core unit which includes a multiplicity of integral pole pieces. The block is of elongated construction and it has a series of spaced apart projections extending transversely to its longitudinal axis to provide discrete pole pieces. A series of elongated bores extend transversely to the longitudinal axis of the block in alignment with each of the projections. A hammer actuator assembly is disposed in each bore. A bucking coil contiguously surrounds each of the projections to provide a series of selectively energizable magnetic fields for operating each hammer actuator. With such an arrangement, the single pole piece block may be readily manufactured and assembled, at reduced cost. In addition, the working distance between tips of hammers and the paper may be readily adjusted by means of a single operation, thus affording a considerable saving in field maintenance time.

United States Patent 1 1 Belser 1 51 May 22,1973

[54] MULTIPLE HAMMER MAGNETIC POLE PIECE BLOCK Primary Examiner-William B. Penn [75] Inventor: Karl Arnold Belser, San Jose, Calif. Atmmey ThmaS Bnody et [73] Assignee: International Business Machines [57] ABSTRACT Corporation, Armonk, N.Y. A print hammer actuating assembly for a hlgh speed Flled! 23, 1971 printer, wherein a one-piece magnetic block is secured [21] Appl. No.: 211,504 to a first core structure to provide a second core unit WhlCh 1ncludes a multiplicity of 1ntegral pole pieces.

The block is of elongated construction and it has a se- [52] US. Cl. "191/93 C, 335/229 ties of spaced apart projections extending transversely [51] Int. Cl. "B411 9/38, "011' 7/04 to its longitudinal axis to provide discrete pole l [58] Field of Search ..10l/93 C, 111; A Series of elongated bores extend transversely to the 335/229 266 longitudinal axis of the block in alignment with each of the projections. A hammer actuator assembly is [56] References cued disposed in each bore. A bucking coil contiguously UNlTED STATES PATENTS surrounds each of the projections to provide a series of selectively energizable magnetic fields for operating 3 3'2"" et a] g each hammer actuator. With such an arrangement, the e ms 3,282,203 11/1966 Kaibach et 31.. .....101/93 c smgle may be readlll. .manufacw'ed 3 385 2 5/1968 Shepard 101/93 C and assembled, at reduced cost. In addition, the work- 3:460:469 8/1969 Brown [93 C ing distance between tips of hammers and the paper 3,468,246 9/1969 Lee etal. ..101/93 c y be ea i y a ju ted by means of a single opera- 3,556,002 1/1971 Bragg ..101/93 C tion, thus affording a considerable saving in field 3,636,865 1/1972 Konkel ..l0l/93 C maintenance time. 3,656,425 4/1972 Albo et a]. ..l0l/93 C 3,659,238 4/1972 Grifflin ..335/229 6 Claims, 4 Drawing Figures l I05 99 I, I0 3 67 7911 111 99 61 l ill 3 115 L 5 .2 113 PATENTEL RAY 2 2 1975 sum 2 OF 3 I I f/l L FIG.3

PATENIEL HUB i973 SHEET 3 []F 3 MULTIPLE HAMMER MAGNETIC POLE PIECE BLOCK BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a print hammer actuating assembly for a high speed chain printer, and more particularly to a pole piece structure for operating a series of hammer actuators in high speed chain printers.

2. Description of the Prior Art In chain printers of the type commonly used today, a chain of uniformly spaced apart type slugs is moved at constant speed in a continuous path. A portion of the path is located on a print line extending transversely of a record receiving web, such as a paper. The paper is fed intermittently, line by line, into registry with the print line by a feed mechanism. A plurality of hammers are located respectively adjacent to print columns in the print line, and are operated selectively by computer controlled electronic filling circuits to impress a selected type character of a print element against a ribbon and paper backed by a platen, as the type character moves into registry with a print column near which the selected hammer is located.

Typical prior art hammer assemblies for chain printers consist of a movable impact device which is associated with a solenoid so that upon energization or deenergization of the solenoid coil, a solenoid armature or the like is driven against the impact device or hammer to thereby propel it against the paper. In attempting to significantly increase the speed of the printing devices, problems arise involving the coupling between the solenoid armature and the impact device. In an effort to solve these problems, improved hammer assemblies have been introduced, such as that disclosed in US. Pat. 3,460,469. The hammer assembly shown in the cited patent uses a core structure which is formed with a U-shaped member and a substantially straight member attached thereto. The U-shaped member and the straight member provide a pair of laterally offset pole pieces. One pair of such pole pieces, involving at least two elements for the core structure, is provided for the actuation of each hammer. The straight member of the aforementioned core structure is fastened to the U- shaped member by means of two screws. The adjustment of these screws helps to determine the relative position of the laterally offset pole pieces. Other prior art hammer actuating techniques for chain printers have usually required the use of separate and distinct pole piece parts for each individual hammer. This, of necessity, requires individual adjustments of the pole faces for each printing hammer, thus adding undesirably to assembly costs and field maintenance time for the overall printing device.

It has therefore been found desirable to provide a new and improved type of hammer actuating mechanism which involves improved adjustability, a reduced number of parts, and lower assembly costs.

SUMMARY OF THE INVENTION An important object of this invention is to provide an improved print hammer assembly for a high speed chain printer, which is simplified in construction and economical in cost.

Another object of this invention is to provide an improved hammer actuating mechanism for a high speed printer, which includes a unitary magnetic block that provides a multiplicity of pole pieces thereon.

A further object of the present invention is to provide an improved magnetic core structure for a high speed chain printer, which is capable of receiving a multiplicity of hammer actuating mechanisms, and efficiently supporting a series of coils for operating these hammer actuating mechanisms.

In carrying out my invention, in one form thereof, it is applied to a high speed chain printer which includes a continuous belt that drives a plurality of printing ele ments past a printing line for actuation by printing hammers. The printing hammer assembly includes a first core structure and a one piece magnetic block secured to the first core structure to provide a second core structure. The one piece block is of elongated construction and has a series of spaced apart projections extending transversely from its longitudinal axis to provide a series of discrete pole pieces formed integrally on the block. A series of elongated bores are formed in the block so that they extend in relative parallel relationship to each other, and transversely to the longitudinal axis of the block. The bores are in alignment with each of the projections. A hammer actuator assembly is disposed in each bore so that it is extendable outwardly through the projection. An individual bucking coil contiguously surrounds each projection to provide a magnetically energizable field for releasing the hammer actuator. A holding coil circumscribes the first magnetic core structure.

With such an arrangement, the holding coil is energized to generate a magnetic flux in the first and second core structures for continuously attracting the hammer armature toward its inactive position. The bucking coil of each hammer is selectively energized for a predetermined time to generate a flux in opposition to the flux produced by the holding coil, for releasing the movable hammer armature. By using a unitary magnetic pole piece block for the print hammer assembly, a considerable savings is achieved in manufacturing costs and field maintenance time. The single pole piece block also enables each hammers magnetic circuit to have a relatively low reluctance, thereby enhancing its efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects, features and advantages of this invention will be apparent from the following description of the drawings in which:

FIG. 1 is a front view, with some parts cut away, of a chain printer embodying my invention;

FIG. 2 is an enlarged view of a portion of the print chain assembly, partially broken away, to show in greater detail the interrelationships of the unitary pole piece block, printing hammers, solenoid coil and pole pieces;

FIG. 3 is a sectional view, partially broken away, of the printer of FIG. 1; and

FIG. 4 is a fragmentary perspective view of the unitary pole piece block, with a hammer and a hammer ac tuator assembly exploded therefrom.

DETAILED DESCRIPTION Referring now to the drawings, there is shown in FIGS. 1, 2 and 3 a front printing chain printer 9 having a type carrier 1 1 which travels in a substantially vertical plane in front of a series of print hammers 13. A series of printing elements are mounted on the type carrier 11. Each of the printing elements 15 resembles a hand having four flexibly movable fingers 17 (FIG. 1). The finger 17 has a type slug 19 secured to one of its faces near the free end thereof, to produce the selected character when each finger 17 is struck by the print hammer 13. The type slug or character is pressed into engagement with a ribbon 21 and a record member 23 (FIG. 1) that is backed by a suitable platen member 25. The hammers 13 have faces 13a which each traverse the span of a plurality of adjacent print positions. Control of the printing is accomplished by a suitable hold coil 27 which holds all hammers 13 in the retracted inoperative position and individual bucking coils 29 which are selectively actuated to release and cause the associated hammer to complete a cycle of operation. The printing slug 19 of the printing finger 17 selected is aligned before an appropriate protrusion on the face of the print hammer 13 so that the appropriate selected type slug 19 may be printed while the other type slugs 19 are not contacted by the hammer face and are consequently not printed. When the hammer 13 strikes the type slugs 19 onto the platen member 25, the hammer rebounds and the hold coil 27 flux reattracts the hammer to the inoperative position so that the hammer is then in a position to be selected for another printing operation. The signal to energize the bucking coils 29 is generated by suitable control means. This control means provides stored coded data of the text to be printed for a complete line and this data is compared with the coded data representing the print element in position for printing at each print position. This print element position is established by the combination of a home pulse generated by the appropriate hand, and a column-by-column emitter at the input drive shaft. An equal compare produces a signal which is coupled to actuate the proper print hammer for printing the designated character at the designated print position. A similar operation is conducted at each time designated characters on the chain reach a print position, until the complete line is printed.

As further shown in FIG. 1, the printer comprises a cartridge 31 wherein there is located the type carrier 11 mounted to be driven by a pair of sprocket wheels 33. The wheels 33 are driven from a suitable drive motor 34. The cartridge 31 includes a front housing portion and a rear housing portion which are suitably fastened together to provide a compact type of removable support for the type carrier 11 and its printing elements 15.

The rear housing portion of the cartridge provides a base for supporting the type carrier and the printing elements l5, and the front housing portion of the cartridge provides a cover for enclosing the carrier mechanism in the housing. When the front and rear housing portions of the cartridge are fastened together, they provide a suitable guide surface that acts to control the path of movement of the printing elements 15.

To provide an efficient and economical means for selectively actuating the various hammers 13 of the printer, in accordance with my invention, first and second elongated core assemblies 35, 37 are provided. The first core assembly 35, as shown in FIG. 3, includes an elongated L-shaped base 39 of magnetic material, an elongated flat hammer guiding element 41 attached to the top 43 of one side of the elongated base 39, and

a relatively short L-shaped upper element 43, secured to the hammer guiding section by suitable screws.

As further shown in FIG. 3, the upper element 43 of the first core assembly includes a horizontal portion 45, and a vertical portion 49. Adjacent the corner described by the horizontal portion 45 and vertical portion 49 of the upper element 43 of core assembly 35, there is formed in the flat hammer guiding section 41 a series of spaced apart bores 47. (See also FIG. 4) The bores 47 are for receiving the smooth cylindrically configured bases 51 of the hammers 13. Thus, more particularly, as shown in FIG. 4, the external diameter of the bases 51 of the hammers 13 is of a slightly lesser dimension than the diameter of the bores 47 of core section 41. The base 51 of each hammer is connected to a relatively thin shank 53, which in turn is connected to the center of the hammer head 55.

For guiding the movement of the hammer in a direction parallel to the axis of the bores 47, in addition to the sliding cooperation of the smooth outer surface of the cylindrical base 51 of each hammer with its associated bore 47, there is provided an elongated rib 57, which projects parallel tothe flat section 41, and is disposed in overlying relationship thereto. The rib 57 has a series of open slots 59 formed therein (FIG. 4). The slots 59 are in axial alignment with the bores 47 so that they may receive and guide the sliding movement of the shanks 53 as the cylindrical bases 51 of the hammers slide within their associated bores 47.

As thus shown in FIGS. 2 and 3, the first elongated core assembly 35 serves to provide a generally U- shaped core structure together with an upper tier for supporting the print hammers 13. In addition to providing a guiding function for the shanks 53 of the hammers (via slots 59), the elongated rib 57 also serves to limit the movement of the hammer downwardly, or away from the paper (viewing FIG. 2).

Turning now to the second core assembly 37, in accordance with the present invention, this assembly includes a unitary or one piece magnetic element 61 (as shown in FIG. 4), constructed, by way of example, from silicon iron (2.5 percent) which is formed to provide a series of integral pole pieces 63 for actuation of the various hammers 13.

More particularly, as best shown in FIG. 4, the one piece element 61 includes an elongated base portion 64 having a generally rectangular cross section, and comprising bottom surface 65, top surface 67, and relatively flat and opposed elongated sides 69 and 71 (FIG. 3). In the top surface 67 of element 61, there is accurately located a series of rectangularly configured projections 73. Each of the projections 73 includes two parallel sides 75, 77 which extend generally perpendicularly to elongated sides 69 and 71, and front and rear surfaces 79 and 81, respectively, which are generally parallel to the elongated sides 69 and 71 and conterminous with the sides 75, 77.

For helping to position solenoid coils 83 on the pole pieces 63, the front and rear surfaces 79 and 81 of the rectangular core projections 73 which furnish the pole pieces, each include shoulders 79a and 81a for supporting an insulating bobbin 85 of an associated coil.

The bobbin 85 of each solenoid coil 83 has a generally rectangular opening 89 formed therein, which is structured to accurately cooperate with sides 75, 77 and front and rear surfaces 79, 81 of the rectangular pole piece projections 73. Thus, as shown in FIGS. 3

and 4, the bobbin 85 of each coil fits snugly into cooperative engagement with the rectangular core projection 73, with the front and rear bottom surfaces of the lower flange of the bobbin 85 engaging shoulder 79a, 81a of the front and rear surfaces 79, 81 respectively.

In the bottom surface 65 of the unitary pole piece element 61, there is located in spaced apart relationship, a series of bores 91, which extend from bottom surface 65 to top surface 67. More particularly, the bores 91 are disposed in spaced apart parallel relationship, with the main lower portion 93 of each bore 91 having a somewhat larger diameter than the upper portion 95 thereof. The upper portion 95 of each bore extends outwardly through the rectangular projection 73 to facilitate the actuation of the hammer 13.

As further shown in FIGS. 3 and 4, near the bottom of lower portion 93 of each bore 91, there is formed an internal thread for the purpose of receiving a set screw 97. The hammer actuator assembly is inserted in each of the bores 91, with a plunger 99 being first inserted. (See FIG. 4) The plunger 99 has a cylindrical upper section 101 (FIG. 2) connected to a cylindrical lower section 103 having a larger external diameter than the upper section 101. The cylindrical upper section 101 of the plunger 99 is in slidable cooperative engagement with the upper portion 95 of bore 91, and the cylindrical lower section 103 of the plunger is in slidable cooperation with the main lower portion 93 of the bore 91. Annular shoulder 105 of the plunger 99, which connects the upper section 101 to the lower section 103, engages an annular shoulder 107 between the lower and upper portions 93, 95 of the bore 91, to provide a stop for the upper movement of the plunger 99 in the bore 91. The bottom 109 of lower section 103 of plunger 99 includes an annular projection which furnishes a seat for the upper end of a coiled compression spring 111. Spring 111 is inserted into the bore 91 after the plunger 99, followed by a slidable intermediate element 113, and the aforementioned set screw 97. The intermediate slidable element 113 has a projection 115 formed on its upper surface to seat the bottom of the coiled compression spring 111.

It will thus be seen that the plunger 99, spring 111, intermediate element 113, and set screw 97, all form a hammer actuator assembly which is located inside of the bore'9l of unitary element 61. One of these assemblies is provided for the actuation of each of the hammers 13 of the printing device 9.

For generating a magnetic flux in the first and second core assemblies to attract the hammer base or armature 51 towards the pole piece 63, the aforementioned hold coil 27 has been provided. Hold coil 27, as shown in FIGS. 2 and 3, circumscribes the lower horizontal section 39a (FIG. 3) of the L-shaped base 39 of the first core assembly 35.

Turning now to a description of the operation of the hammer 13 of the printer 9 by means of the first and second core assemblies 35, 37 and their associated hammer actuating mechanisms, attention is directed to FIG. 2. For each of the thirty three hammers of the chain printer, the holding coil 27 is normally energized to generate a magnetic flux inthe first and second magnetic core structures. This magnetic flux tends to continuously attract each hammer armature 51 toward an associated pole piece 63. For the hammer assembly shown to the right of the two hammer assemblies illustrated by broken away lines in FIG. 2, since its associated bucking coil 29 is not energized, the holding coil 27 produces a flux at pole piece 63 which attracts the hammer armature 51 toward pole piece 63. This holds the head 55 of the hammer in its retracted position and loads the compressive force of spring 111.

For firing the hammer, attention is directed to the hammer actuating assembly shown on the left side of the two broken away hammers in FIG. 2. For this condition, the bucking coil 29 associated with the hammer 13, has been energized for a predetermined time to generate a flux which is in opposition to the flux produced by the holding coil 27. The flux generated by the bucking coil 29 is of such a magnitude as to overcome the attractive force exerted upon the hammer armature 51 so that the compression spring 111 exerts sufficient force upon plunger 99 to push the upper cylindrical section 101 of plunger 99 through upper portion 95 of the bore 91. The top of upper section 101 of the plunger 99 imparts a force upon the hammer armature 51 to rapidly thrust the hammer upwardly. This hammer is then in its fired position. (FIG. 2)

By rotation of the set screw 97 of each hammer actuating assembly, the forward flight time of each hammer may be readily adjusted.

One of the advantages residing in the use of the present invention is that the working distance between the tips (i.e., faces) 13a of all hammers and the paper 21 (FIG. 3) may be adjusted in a single operation, such as by pivoting or translating the core assembly 35 with respect to the paper. In addition, by mounting the unitary pole piece element 61 to the first core assembly 35, the face of each of the pole pieces 63 is automatically kept in parallel and aligned relationship relative to the faces of the hammer armatures 51. In most prior art mechanisms of this type, individual pole pieces had to be adjusted for parallelism with respect to individual hammer armature faces.

A further advantage of the present invention is that the bucking coils 29 are located in extremely close proximity around the hammer armature 51. This tends to minimize the forward flight time for each of the hammers. It has also been found that by using a unitary pole piece block for core assembly 37, and thereby providing all of the pole pieces of the various solenoids, a relatively large bore size may thus be used for the hammer actuating assembly. This relatively large bore size enables the device to accommodate stiffer and/or concentric springs without the necessity of increasing pole tip size. Another significant advantage of the present invention is that each hammers magnetic circuit has a significantly lower reluctance. This tends to reduce the needed drive requirement for each hammer.

It will now therefore be seen that I have provided a new and improved magnetic pole piece block for a multiple hammer chain printer type of mechanism. This structure readily lends itself to economical manufacturing costs, and improved field maintenance. It is particularly advantageous in a chain printer type application.

While in accordance with the Patent Statutes, I have described what at present is considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes or modifications may be made therein without departing from the present invention.

What I claim is:

i ll. A print hammer assembly for a high speed printer, said assembly comprising:

a supporting structure;

a series of spaced apart hammers slidably arranged in said support;

a unitary magnetic pole piece block secured to said supporting structure;

said block being of elongated configuration, having a longitudinal axis, and also including a series of spaced apart projections extending transversely to the longitudinal axis of said block from a first elongated surface of said block to provide a series of discrete spaced apart pole pieces formed integrally thereon, and

a series of elongated bores one of which extends transversely to the longitudinal axis of said block in alignment with each of said projections;

said bores each extending from a second longitudinal surface of said block opposite said first longitudinal surface thereof, and emerging from said first longitudinal surface in alignment with the center of the extremity of said projection;

a hammer actuator assembly disposed in each said bore and extending outwardly through said projection for operative engagement with an associated hammer;

coil means contiguously surrounding each said projection thereby to provide a magnetically energizable field for operating said hammer actuator assembly;

and means to selectively energize said coil means for a predetermined time to generate a flux thereby to operate said hammer actuator assembly into engagement with said hammer.

2. A print hammer assembly for a high speed printer,

said assembly comprising:

a first magnetic core structure;

a unitary magnetic pole piece block secured to said first core structure thereby to provide a second core structure;

said block being of elongated configuration and having a longitudinal axis;

said block further including a series of spaced apart projections extending transversely to the longitudinal axis of said block from one elongated side of said block to provide discrete pole pieces formed integrally thereon, and

a series of elongated bores one of which extends transversely to the longitudinal axis of said block in alignment with each of said projections;

said bores each extending from one longitudinal side of said block and emerging from another and opposite side of said block in alignment with the center of the extremity of said projection;

a hammer actuator assembly disposed in each said bore and extending outwardly through said projection;

bucking coil means contiguously surrounding each said projection thereby to provide a magnetically energizable field for releasing said hammer actuator; and

holding coil means circumscribing said first magnetic core structure;

means for energizing said holding coil means and generating a magnetic flux in said first and second magnetic core structures to attract a hammer armature toward said pole pieces, and

means to selectively energize said bucking coil means for a predetermined time to generate a flux in opposition to the flux produced by said holding coil means thereby to release said movable hammer armature.

3. The print hammer assembly of claim 2, wherein the block has a relatively flat oblong shaped cross section with first and second opposed sides of substantially greater dimension than third and fourth opposed sides; said projections being located in uniformly spaced apart relationship along said third side,

the bores for receiving the hammer actuator assemblies extending in a direction parallel to said first and second sides and emerging outwardly through said third and fourth sides.

4. The print hammer assembly of claim 3, wherein the projections have a generally rectangular perimeter and the bucking coil means comprises a series of individual coils, each of said coils having an insulative bobbin with a rectangular passageway formed therein for cooperation with the external perimeter of an associated projection.

5. The print hammer assembly of claim 4, wherein a means is included for concurrently adjusting the dimensional relationship between the pole faces of said block projections and associated hammers of the high speed printer.

6. A high speed chain printer comprising a pair of sprocket wheels means for rotatably supporting said wheels on spaced parallel axes;

a print chain trained about said wheels;

said print chain including an endless belt and a plurality of printing elements spaced along the outer surface of said belt and carried thereby;

a plurality of hammers having heads capable of impacting upon said printing elements to print upon a web;

each of said hammers also including a hammer arma- I ture; and a print hammer actuating assembly comprising a first magnetic core structure; a unitary magnetic pole piece block secured to said first core structure, thereby to provide a second core structure; said block being of elongated configuration, having a longitudinal axis, and also including a series of spaced apart projections extending transversely to the longitudinal axis of said block to provide a series of discrete spaced apart pole pieces formed integrally thereon, and

a series of elongated bores one of which extends transversely to the longitudinal axis of said block in alignment with each of said projections;

said bores each extending from a second longitudinal surface of said block opposite said first longitudinal surface thereof, and emerging from said first longitudinal surface in alignment with the center of the extremity of said projection;

a hammer actuator assembly disposed in each I said bore and extending outwardly through its associated projection for operative engagement with an associated hammer;

holding coil means circumscribing said first magnetic core structure;

a series of bucking coils, one of which contiguously surrounds each said projection, thereby to provide a magnetic field energizable for releasing said hammer actuator;

means for energizing said holding coil means for generating a magnetic flux in said first and second magnetic core structures to attract the hammer armatures toward their associated pole 

1. A print hammer assembly for a high speed printer, said assembly comprising: a supporting structure; a series of spaced apart hammers slidably arranged in said support; a unitary magnetic pole piece block secured to said supporting structure; said block being of elongated configuration, having a longitudinal axis, and also including a series of spaced apart projections extending transversely to the longitudinal axis of said block from a first elongated surface of said block to provide a series of discrete spaced apart pole pieces formed integrally thereon, and a series of elongated bores one of which extends transversely to the longitudinal axis of said block in alignment with each of said projections; said bores each extending from a second longitudinal surface of said block opposite said first longitudinal surface thereof, and emerging from said first longitudinal surface in alignment with the center of the extremity of said projection; a hammer actuator assembly disposed in each said bore and extending outwardly through said projection for operative engagement with an associated hammer; coil means contiguously surrounding each said projection thereby to provide a magnetically energizable field for operating said hammer actuator assembly; and means to selectively energize said coil means for a predetermined time to generate a flux thereby to operate said hammer actuator assembly into engagement with said hammer.
 2. A print hammer assembly for a high speed printer, said assembly comprising: a first magnetic core structure; a unitary magnetic pole piece block secured to said first core structure thereby to pRovide a second core structure; said block being of elongated configuration and having a longitudinal axis; said block further including a series of spaced apart projections extending transversely to the longitudinal axis of said block from one elongated side of said block to provide discrete pole pieces formed integrally thereon, and a series of elongated bores one of which extends transversely to the longitudinal axis of said block in alignment with each of said projections; said bores each extending from one longitudinal side of said block and emerging from another and opposite side of said block in alignment with the center of the extremity of said projection; a hammer actuator assembly disposed in each said bore and extending outwardly through said projection; bucking coil means contiguously surrounding each said projection thereby to provide a magnetically energizable field for releasing said hammer actuator; and holding coil means circumscribing said first magnetic core structure; means for energizing said holding coil means and generating a magnetic flux in said first and second magnetic core structures to attract a hammer armature toward said pole pieces, and means to selectively energize said bucking coil means for a predetermined time to generate a flux in opposition to the flux produced by said holding coil means thereby to release said movable hammer armature.
 3. The print hammer assembly of claim 2, wherein the block has a relatively flat oblong shaped cross section with first and second opposed sides of substantially greater dimension than third and fourth opposed sides; said projections being located in uniformly spaced apart relationship along said third side, the bores for receiving the hammer actuator assemblies extending in a direction parallel to said first and second sides and emerging outwardly through said third and fourth sides.
 4. The print hammer assembly of claim 3, wherein the projections have a generally rectangular perimeter and the bucking coil means comprises a series of individual coils, each of said coils having an insulative bobbin with a rectangular passageway formed therein for cooperation with the external perimeter of an associated projection.
 5. The print hammer assembly of claim 4, wherein a means is included for concurrently adjusting the dimensional relationship between the pole faces of said block projections and associated hammers of the high speed printer.
 6. A high speed chain printer comprising a pair of sprocket wheels means for rotatably supporting said wheels on spaced parallel axes; a print chain trained about said wheels; said print chain including an endless belt and a plurality of printing elements spaced along the outer surface of said belt and carried thereby; a plurality of hammers having heads capable of impacting upon said printing elements to print upon a web; each of said hammers also including a hammer armature; and a print hammer actuating assembly comprising a first magnetic core structure; a unitary magnetic pole piece block secured to said first core structure, thereby to provide a second core structure; said block being of elongated configuration, having a longitudinal axis, and also including a series of spaced apart projections extending transversely to the longitudinal axis of said block to provide a series of discrete spaced apart pole pieces formed integrally thereon, and a series of elongated bores one of which extends transversely to the longitudinal axis of said block in alignment with each of said projections; said bores each extending from a second longitudinal surface of said block opposite said first longitudinal surface thereof, and emerging from said first longitudinal surface in alignment with the center of the extremity of said projection; a hammer actuator assembly disposed in each said bore and extending outwardly through its associated projection for opeRative engagement with an associated hammer; holding coil means circumscribing said first magnetic core structure; a series of bucking coils, one of which contiguously surrounds each said projection, thereby to provide a magnetic field energizable for releasing said hammer actuator; means for energizing said holding coil means for generating a magnetic flux in said first and second magnetic core structures to attract the hammer armatures toward their associated pole pieces; and means for selectively energizing certain of the bucking coils for a predetermined time to generate fluxes in opposition to the flux produced by the holding coil means, thereby to release movable hammer armatures from their associated pole pieces and actuate the selected hammers against predetermined printing elements for printing on said web. 